1. Field of the Invention
The present invention concerns a device for holding a substantially parallelepiped part in position, and more especially a device for holding cathode tube screens in position.
For cathode tubes, devices of this type for holding the screens in position or for clamping the screens can be used at any point in the assembly line. However, they are used especially in rooms where luminous substances are deposited on the screen.
2. Description of the Prior Art
As shown in FIG. 1, the devices currently used to hold cathode tube screens in position consist essentially of a base 1 which may be, for example, a rectangular frame with its two big sides each having two fixed supporting points 2 designed to receive the front surface of the screen. Furthermore, on one of the small sides of the base 1, a first supporting element is mounted in a fixed way. This first supporting element consists of a vertical column 3 to an arm 4 is fixed perpendicularly. This arm 4 carries, at each end, a sleeve 5. The sleeve 5 is preferably made of an elastic material such as rubber. A second supporting element, in rotatable on the axis A, is mounted on the other small side of the base 1. This second supporting element consists of a vertical column 3' at the upper end of which an arm 4' is fixed perpendicularly. This arm 4' too has a sleeve 5', made of an elastic material, at its two ends. With this device, the front face of the screen E is placed so as to be supported on the four supporting points 2. Then this screen is moved in translation so that one of the sides of the skirt J of the screen is supported against the two sleeves 5 of the fixed supporting element. During this time, the movable supporting element 3' is kept at a distance to enable the screen to be positioned. Then, the movable supporting element is brought to rest against the other side of the skirt by releasing a spring 6 and a pushbutton 6', thus causing the movable supporting element to be clamped against the screen. Furthermore, the base 1 has a hub designed to receive a vertical shaft 12. This vertical shaft is fixed to an machining head. As shown in FIG. 1, this machining head essentially has a frame 8 to which a perpendicular bracket 9 is fixed. At the end of the bracket, there is fixed a hollow sleeve 11, pivoting on the axis 10. The shaft 12 is inserted in the sleeve 11. It goes through hub 7 and is fixed in position by means of a system with screws. This system enables the setting of the working height of the screen. The term "working height" implies the distance between a pivoting point 10 and a plane P determining the soldering edge of the screen to the cone. This device can work accurately only with screens which all have the same dimensions. The use of a fixed supporting element and a moving supporting element necessitates screens of the same length to obtain precise centering of the screen. If centering of this type is not obtained, large-scale vibrations are observed on the machining head, and this results in a great many manufacturing rejects. Furthermore, during the centering process, there is always a slight slipping of the surface of the screen on the supporting points thus causing grooves on the glass slab. Furthermore, when there are screens of different heights, the working height is not maintained to and certain operations such as soldering or other operations may not be achieved. This type of device therefore limits the flexibility of the assembly line.
SUMMARY OF THE INVENTION
An object of the present invention is to overcome the above-mentioned drawbacks by proposing a new device to hold substantially parallelepiped-shaped parts, such as screens for cathode tubes, in position.
Consequently, an object of the invention is to provide a device for holding a substantially parallelepiped-shaped part in position, said device being of the type comprising the following elements fixed to a base: a supporting device on which the part rests and at least two supporting elements that clamp the part on two opposite sides, wherein the two supporting elements are fixed by a deformable quadrilateral element so that there is a continuously variable distance between the two supporting elements.
According to a preferred embodiment, the deformable quadrilateral element consists of two arms of the same length hinged at their midpoints on the base, and by two side members respectively hinged on the opposite ends of the two arms, a supporting element being fixed to one end of a side member while the other supporting element is fixed to the other end of the other side member.
According to another characteristic of the invention, the device further includes a means for exerting a force on the two supporting elements in a position where they are at a minimum distance from each other. This means for exerting force on the two supporting elements, in their position where they are at a minimum distance from each other, consists of at least one spring fixed between the two supporting elements. Preferably, the means for exerting force on the two supporting elements, in their position where they are at a minimum distance from each other, consists of two springs each fixed by a supporting element and the end of the side member of the other supporting element. With this device, precise centering of the part is obtained regardless of its dimensions.
According to another characteristic of the present invention, the supporting device comprises means for the pre-positioning of the part, said means being solidly joined to the base, and at least three supporting points fixed to the base so as to be capable of being shifted vertically.
According to a preferred embodiment, each supporting point is designed to be at the end of a lever hinged on the base, the position of said lever being fixed by a stop which is solidly joined with one of the side members. This arrangement of supporting points enables the adjustment of the working height according to the height of the parallelepiped shaped part.